The present invention relates generally to a new family of antennas with a multiband behaviour and a reduced size. The general configuration of the antenna consists of a multilevel structure which provides the multiband behaviour, combined with a multilevel and/or space-filling ground-plane. A description on Multilevel Antennas can be found in Patent Publication No. WO01/22528. A description on several multilevel and space-filling ground-planes is disclosed in Patent Application PCT/EP01/10589. In the present invention, a modification of said multilevel structure is introduced such that the frequency bands of the antenna can be tuned simultaneously to the main existing wireless services. In particular, the modification consists of splitting the multilevel structure in two arms of different length that follow a winding parallel path spaced by a winding parallel gap (parallel to the arms) with a substantially similar shape as each of said arms, that is, with a similar winding path as the arms. Also, when the multilevel antenna structure is combined with a multilevel and/or space-filling ground-plane, the overall performance of the antenna is enhanced, increasing the bandwidth and efficiency of the whole antenna package. Due to the small size, high efficiency and broad band behaviour of the antenna, it is especially suitable for, but not limited to, the use in small handheld terminals such as cellular phones, PDAs or palm-top computers.
Although publications WO01/22528 and WO01/54225 disclose some general configurations for multiband and miniature antennas, an improvement in terms of size, bandwidth, and efficiency is obtained in some applications when said multilevel antennas are set according to the present invention. Such an improvement is achieved mainly due to the particular two-arm multilevel geometry of the antenna, used in conjunction with the design of the ground-plane and the interaction of both. Also, in some embodiments the antenna features a single feeding point and no connection to the ground-plane is required, which introduces a significant advantage in terms of manufacturing cost and mechanical simplicity.
A multilevel structure for an antenna device, as it is known in prior art, consists of a conducting structure including a set of polygons, all of said polygons featuring the same number of sides, wherein said polygons are electromagnetically coupled either by means of a capacitive coupling or ohmic contact, wherein the contact region between directly connected polygons is narrower than 50% of the perimeter of said polygons in at least 75% of said polygons defining said conducting multilevel structure. In this definition of multilevel structures, circles, and ellipses are included as well, since they can be understood as polygons with a very large (ideally infinite) number of sides. An antenna is said to be a multilevel antenna, when at least a portion of the antenna is shaped as a multilevel structure.
A space-filling curve for a space-filling antenna, as it is known in prior art, is composed by at least ten segments which are connected in such a way that each segment forms an angle with their neighbours, i.e., no pair of adjacent segments define a larger straight segment, and wherein the curve can be optionally periodic along a fixed straight direction of space if and only if the period is defined by a non-periodic curve composed by at least ten connected segments and no pair of said adjacent and connected segments define a straight longer segment. Also, whatever the design of such SFC is, it can never intersect with itself at any point except the initial and final point (that is, the whole curve can be arranged as a closed curve or loop, but none of the parts of the curve can become a closed loop).
In some particular embodiments of the present invention, the antenna is tuned to operate simultaneously at four bands, those bands being for instance GSM850, GSM900, DCS1800, and PCS1900. In other embodiments the antenna is able to cover also the UMTS band. There is not an example described in the prior art of an antenna of this size covering such a broad range of frequencies and bands.
The combination of said services into a single antenna device provides an advantage in terms of flexibility and functionality of current and future wireless devices. The resulting antenna covers the major current and future wireless services, opening this way a wide range of possibilities in the design of universal, multi-purpose, wireless terminals and devices that can transparently switch or simultaneously operate within all said services. For instance, the simultaneous coverage of the GSM850, GSM900, DCS1800, and PCS1900 provides to a cell phone user with the ability to connect transparently to any of the two existing European GSM bands (GSM900 and DCS1800) and to any of the two American GSM bands (PCS1900 and the future GSM850).